SQLSERVER中的自旋锁
SQLSERVER中的自旋锁 在SQLSERVER中的锁有很多,例如什么意向共享锁,排他锁,行,页锁 这些都属于LOCK 而latch比lock更轻量级,只在内存中存在,一般用来锁住数据页面,防止多人同时修改内存中的一个数据页面 而今天介绍的spin lock则比上面两种锁更更轻量
SQLSERVER中的自旋锁
在SQLSERVER中的锁有很多,例如什么意向共享锁,排他锁,行,页锁 这些都属于LOCK
而latch比lock更轻量级,只在内存中存在,一般用来锁住数据页面,防止多人同时修改内存中的一个数据页面
而今天介绍的spin lock则比上面两种锁更更轻量级的
spin lock介绍:
lock和latch以外还有一种更轻量级的同步资源:spin lock(自旋锁),第一次看到spin lock这个名词是在潘爱民老师写的
《Windows内核原理与实现》这本书里看到的,估计SQLSERVER也借鉴了Windows操作系统的一些同步技术。
在SQLSERVER里,有些spin lock很快就能得到也很快会被释放,一般来讲不大会发生长时间等待的同步资源,
SQLSERVER选择让线程在CPU上稍微等一会(所谓自旋),而不是将CPU资源让出来。由于资源很快能够得到,
这样处理能够减少CPU上线程的切换,更有效率(Windows也是这样做的减少线程切换的开销,经常切换线程上下文是很耗费CPU资源的)
自旋锁有可能带来的一些瓶颈:
像latch一样,spin lock是一种很轻量级的资源,正常情况下不应该成为SQLSERVER的瓶颈。当看到SQLSERVER中存在很多任务都是running
或者runnable状态可能就是spin lock的原因。在SQLSERVER内部,自旋锁的种类还是挺多的。在SQLSERVER2005里有172种那么多
大家可以运行下面语句,得到SQLSERVER在所有自旋锁上等待的次数
<span>1</span> DBCC SQLPERF(spinlockstats)

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